Using conditional power of network meta‐analysis (NMA) to inform the design of future clinical trials

Clinical trials are typically designed with an aim to reach sufficient power to test a hypothesis about relative effectiveness of two or more interventions. Their role in informing evidence‐based decision‐making demands, however, that they are considered in the context of the existing evidence. Consequently, their planning can be informed by characteristics of relevant systematic reviews and meta‐analyses. In the presence of multiple competing interventions the evidence base has the form of a network of trials, which provides information not only about the required sample size but also about the interventions that should be compared in a future trial. In this paper we present a methodology to evaluate the impact of new studies, their information size, the comparisons involved, and the anticipated heterogeneity on the conditional power (CP) of the updated network meta‐analysis. The methods presented are an extension of the idea of CP initially suggested for a pairwise meta‐analysis and we show how to estimate the required sample size using various combinations of direct and indirect evidence in future trials. We apply the methods to two previously published networks and we show that CP for a treatment comparison is dependent on the magnitude of heterogeneity and the ratio of direct to indirect information in existing and future trials for that comparison. Our methodology can help investigators calculate the required sample size under different assumptions about heterogeneity and make decisions about the number and design of future studies (set of treatments compared).     

An efficient and optimized purification procedure for the superoxide dismutase from Aspergillus niger. Partial characterization of the purified enzyme

Cu, Zn-superoxide dismutase was isolated from Aspergillus niger mycelia, harvested at the mid-logarithmic growth phase. The purification scheme aimed at the optimization of the ethanol/chloroform extraction (Tsuchihashi extraction) through response surface methodology. Upon optimum extraction conditions, it was possible to obtain electrophoretically pure enzyme preparations, by the application of one step anion exchange chromatography. The enzyme yield of this simple purification procedure was above 75% while the specific activity of the final preparation was among the highest reported for eucariotic microorganisms. The purified enzyme exhibited similar physicochemical characteristics with other Aspergillus sp. superoxide dismutases revealing an apparent tetrameric structure with a subunit molecular weight of 19 kDa, and a pl of 5.95.This revised version was published online in October 2005 with corrections to the Cover Date.     

Interactions of angiotensin II with membranes using a combination of differential scanning calorimetry and 31P NMR spectroscopy

Summary This study of angiotensin II (ANG II) membrane interactions uses a combination of³¹P NMR spectroscopy and differential scanning calorimetry (DSC), two valuable and complementary techniques which can provide useful information about the thermotropic and dynamic properties of peptide hormones in membranes. The major conclusion from the calorimetric experiments is that ANG II affects the phase properties of hydrated dipalmitoyl-phosphatidylcholine (DPPC) bilayers by mainly broadening the pretransition area. Preliminary³¹P NMR data seem to confirm the DSC results by showing that ANG II produces a lowering of the pretransition temperature but affects only minimally the main phase transition. In combination, the results from the two methods may indicate that the hormone produces its effects on the phospholipid head groups while its effects on the bilayer alkyl chains are not significant. Such results can be interpreted to mean that ANG II closely interacts with the phospholipid head groups perhaps up to the level of the interface, but does not enter deeper into the membrane bilayer.     

Extensions of the probabilistic ranking metrics of competing treatments in network meta-analysis to reflect clinically important relative differences on many outcomes

One of the key features of network meta-analysis is ranking of interventions according to outcomes of interest. Ranking metrics are prone to misinterpretation because of two limitations associated with the current ranking methods. First, differences in relative treatment effects might not be clinically important and this is not reflected in the ranking metrics. Second, there are no established methods to include several health outcomes in the ranking assessments. To address these two issues, we extended the P-score method to allow for multiple outcomes and modified it to measure the mean extent of certainty that a treatment is better than the competing treatments by a certain amount, for example, the minimum clinical important difference. We suggest to present the tradeoff between beneficial and harmful outcomes allowing stakeholders to consider how much adverse effect they are willing to tolerate for specific gains in efficacy. We used a published network of 212 trials comparing 15 antipsychotics and placebo using a random effects network meta-analysis model, focusing on three outcomes; reduction in symptoms of schizophrenia in a standardized scale, all-cause discontinuation, and weight gain.     

A characterization of missingness at random in a generalized shared‐parameter joint modeling framework for longitudinal and time‐to‐event data,and sensitivity analysis

We consider a conceptual correspondence between the missing data setting, and joint modeling of longitudinal and time‐to‐event outcomes. Based on this, we formulate an extended shared random effects joint model. Based on this, we provide a characterization of missing at random, which is in line with that in the missing data setting. The ideas are illustrated using data from a study on liver cirrhosis, contrasting the new framework with conventional joint models.     

Biochemical and catalytic properties of two intracellular β-glucosidases from the fungus Penicillium decumbens active on flavonoid glucosides

In the presence of rutin as sole carbon source, Penicillium decumbens produces two intracellular β-glucosidases named G_I and G_II, with molecular masses of 56,000 and 460,000 Da, respectively. The two proteins have been purified to homogeneity. G_I and G_II composed of two and four equal sub-units, respectively and displayed optimal activity at pH 7.0 and temperature 65–75 °C. Both β-glucosidases were competitively inhibited by glucose and glucono-δ-lactone. G_I and G_II exhibited broad substrate specificity, since they hydrolyzed a range of (1,3)-, (1,4)- and (1,6)-β-glucosides as well as aryl β-glucosides. Determination of k_cat/K_m revealed that G_II hydrolyzed 3–8 times more efficiently the above-mentioned substrates. The ability of G_I and G_II to deglycosylate various flavonoid glycosides was also investigated. Both enzymes were active against flavonoids glycosylated at the 7 position but G_II hydrolyzed them 5 times more efficiently than G_I. Of the flavanols tested, both enzymes were incapable of hydrolyzing quercetrin and kaempferol-3-glucoside. The main difference between G_I and G_II as far as the hydrolysis of flavanols is concerned, was the ability of G_II to hydrolyze the quercetin-3-glucoside.     

A chemical screen for modulators of mRNA translation identifies a distinct mechanism of toxicity for sphingosine kinase inhibitors

We here conducted an image-based chemical screen to evaluate how medically approved drugs, as well as drugs that are currently under development, influence overall translation levels. None of the compounds up-regulated translation, which could be due to the screen being performed in cancer cells grown in full media where translation is already present at very high levels. Regarding translation down-regulators, and consistent with current knowledge, inhibitors of the mechanistic target of rapamycin (mTOR) signaling pathway were the most represented class. In addition, we identified that inhibitors of sphingosine kinases (SPHKs) also reduce mRNA translation levels independently of mTOR. Mechanistically, this is explained by an effect of the compounds on the membranes of the endoplasmic reticulum (ER), which activates the integrated stress response (ISR) and contributes to the toxicity of SPHK inhibitors. Surprisingly, the toxicity and activation of the ISR triggered by 2 independent SPHK inhibitors, SKI-II and ABC294640, the latter in clinical trials, are also observed in cells lacking SPHK1 and SPHK2. In summary, our study provides a useful resource on the effects of medically used drugs on translation, identified compounds capable of reducing translation independently of mTOR and has revealed that the cytotoxic properties of SPHK inhibitors being developed as anticancer agents are independent of SPHKs.

A chemical screen to evaluate how 4100 drugs modulate translation rates confirms mTOR as the main pathway regulating translation and reveals that sphingosine kinase inhibitors downregulate translation via activation of the ER-stress response. Sphingosine kinase inhibitors, including one in clinical trials, activate stress responses and kill cells independently of the cognate target.